Electrical activity sensor device for detecting electrical activity and electrical activity monitoring apparatus

ABSTRACT

An electrical activity monitoring device based on a sensor device attachable to a power cable of an electrical device for monitoring the electrical status of the electrical device. The device comprises an antenna element which performs the dual functions of magnetically coupling with an electrical pulse generated in the power cable in response to a change of electrical power state of the electrical device and to transmit data to a reader via the power cable. An electrical activity monitoring apparatus is also provided for monitoring the electrical status of at least one electrical device connected to a power supply network by a respective power cable provided with a sensor device. The electrical activity monitoring apparatus comprises a reader and a reader-power line interface device.

TECHNICAL FIELD

The present invention relates to an electrical activity sensor devicefor detecting the electrical activity of an electrical device connectedto a power supply network, in particular the change in electrical powerstate. The invention further relates to an electrical activitymonitoring apparatus for monitoring the electrical activity of one ormore electrical devices. The electrical activity sensor device is basedon a radio frequency identification device (RFID).

BACKGROUND

The monitoring of electrical activity of electrical devices finds manyuseful applications in areas such as energy consumption, the building ofuser activity profiles, and in security or safety monitoring systems.For example, in a home environment, knowledge of the activity ofelectrical devices such as a washing machine, lighting devices, acooker, a toaster or a coffee machine may provide useful information onhousehold habits and user activity, enabling a profile to be built up.

A known solution for monitoring the activity of electrical devicesemploys a complex electrical meter system based on remote controlledmodules plugged into power outlets and configured to measure theelectrical consumption of the electrical equipment powered from therespective power outlet. Such, remote controlled modules are typicallyequipped with a wireless communication system based on low powerwireless technology to remotely monitor and control the correspondingelectrical appliance. Such advanced meter systems require howevercomplex and expensive customized installation. Indeed, a recent researchreport on home automation and monitoring has indicated price andtechnical complexity as being the main market hurdles and inhibitorsagainst widespread adoption. Another drawback of such techniques is thatelectrical devices may be moved from one power outlet to another poweroutlet. Moreover, some devices such as lighting devices are not alwayspowered from a power outlet.

Other solutions for the detection of the activity of electrical devicesare based on sensing their “EMI (electromagnetic interference)signature” by monitoring powerlines at one or several points of thepower supply network. These techniques require however a customisedcalibration and training process to learn the EMI signature of variousdevices. Moreover, the EMI signatures may evolve with time. Complexsignal processing techniques are required to disaggregate the signaturesof the various active devices connected to the network and the obtainedresults are not always very accurate.

The present invention has been devised with the foregoing in mind.

SUMMARY

In a general form the invention concerns an electrical activity sensordevice based on antenna device, such as for example a radio frequencyidentification device.

A first aspect of the invention provides an electrical activity sensordevice for monitoring the electrical status of an electrical device, theelectrical activity sensor device comprising: a sensor device attachableto a power cable of the electrical device, the sensor device includingan antenna element operable to magnetically couple with an electricalpulse generated in the power cable by a change in electrical power stateof the electrical device to induce a detectable electrical signal;wherein the antenna element is further operable to transmit datarepresentative of the power state change of the electrical device to areader device via the power cable.

Detection of electrical activity can thus be provided in a simplifiedand low cost manner. The sensor has a dual function of electricalactivity detection and transmission of electrical activity data. Data istypically transmitted to a remote reader in response to interrogation bythe reader via the power supply network. The operational range of thesensor device is extended since data is transmitted to a reader via thepower network rather than wirelessly. Moreover since transmission ofdata is performed via the power cable network, using for example adomestic power infrastructure data transmission is less susceptible tointerference from other wireless systems or to the presence ofobstacles.

A change in the electrical power state of a device may include theswitching ON of the device, the switching OFF of the device, theswitching from a standby mode to an ON power state, and the switchingfrom an ON power state to a standby mode.

In an embodiment the antenna element performs both magnetic coupling tothe electrical pulse and data transmission via the power cable withinits operating frequency range. This provides a simplified detectiondevice since it is not necessary to provide further signal processingfor data transmission.

In an embodiment, the antenna element has a form factor adapted to theshape of the power cable.

In an embodiment, transmission of the data by the antenna elementcomprises backscattering of an RF signal received from the reader devicevia the power cable.

In an embodiment, the sensor device comprises a memory element forstoring, in response to the detected electrical signal the datarepresentative of the power state change of the electrical device andwherein the antenna element is configured to transmit identificationdata identifying the sensor device to the reader device.

In an embodiment, the antenna element is formed as a loop antenna.

In an embodiment, the antenna element is configured to be arrangedaround at least part of the power supply cable to form an inductioncoil. Such a configuration provides more efficient magnetic coupling.

In an embodiment, the device includes a pulse detector configured todistinguish an electrical signal induced from switching on theelectrical device from an electrical signal induced from switching offthe electrical device. For example the pulse detector may be configuredto distinguish between an electrical signal induced from switching ONthe electrical device and an electrical signal induced from switchingOFF the electrical device. Moreover, the pulse detector may beconfigured to distinguish an electrical signal induced from switchingfrom a standby mode to an ON state from an electrical signal inducedfrom switching from an ON state to a standby state. In some particularembodiments the pulse detector may be configured to distinguish betweenelectrical signals induced from switching between an OFF state and an ONstate from those induced switching between a standby mode and an ONstate. In this way information as to the electrical power state isprovided.

In an embodiment, the sensor device comprises an RFID tag operable tocommunication with an RFID reader device.

In an embodiment, the RFID sensor device is operable as a short rangeRFID tag. The short range communication combined with the wiredtransmission via the power network enables power consumption to bereduced with respect to a long range wireless RFID tag system andextended coverage to be provided by transmission via an existing cableinfrastructure.

In an embodiment, the sensor device is operable as a passive sensordevice powered by electromagnetic induction via the power cable. Thisenables power consumption to be reduced by avoiding the use of batterypowered sensors.

In an embodiment the electrical activity sensor device includes anelectrical consumption measurement module for providing datarepresentative of the power consumption of the electrical device whenthe electrical device is switched on and wherein the data transmitted bythe antenna element includes the data representative of the powerconsumption of the electrical device.

In an embodiment the electrical activity sensor device includes a timerto measure the duration of time since the detected change in theelectrical power state of the electrical device.

According to an aspect of the invention there is provided an electricalactivity sensor device for monitoring the electrical status of anelectrical device, the device comprising an RFID sensor deviceattachable to a power cable of the electrical device, the RFID sensordevice including: an antenna element operable to magnetically couplewith an electrical pulse generated in the power cable to generate anelectrical signal in response to a change in the electrical power stateof the electrical device; and a memory element for storing, in responseto the generated electrical signal, data representative of the powerstate change of the electrical device; wherein the antenna element isfurther operable to transmit data representative of the electrical powerstate change of the electrical device and identification dataidentifying the RFID sensor device to an RFID reader device via thepower supply cable.

According to another aspect of the invention there is provided anelectrical activity monitoring apparatus for monitoring the electricalstatus of at least one electrical device connected to a power supplynetwork by a respective power cable provided with an RFID sensor device,the electrical activity monitoring apparatus comprising:

an RFID reader module for transmitting interrogation signals to one ormore RFID sensor devices and for reading identification data and ON/OFFelectrical status data of one or more RFID sensor devices in response tothe interrogation signals, each RFID sensor device being attached to arespective power cable of an electrical device wherein theidentification data and the status data is received from the respectiveRFID sensor device through the power supply network via the respectivepower cable, the electrical status data being representative of thechange in electrical power state of the respective electrical device;and a network interface for electrically coupling the RFID reader moduleto the power supply network and comprising means for extracting datasignals received via the power supply network and insertinginterrogation signals for transmission via the power supply network.

A further aspect of the invention provides a gateway device providing aninterface between an external data communication network and an internaldata communication network comprising an apparatus according to anyembodiment of the second aspect of the invention.

According to a further aspect of the invention there is provided anelectrical activity monitoring system comprising at least one electricalactivity sensor device according to any embodiment of the first aspectof the invention for monitoring the electrical status of an electricaldevice, and an electrical activity monitoring apparatus according to anyembodiment of the second aspect of the invention.

In an embodiment the electrical activity monitoring system furtherincludes an electricity meter connected to the electrical activitymonitoring apparatus for monitoring electrical power consumption in thepower supply network.

According to a further aspect of the invention there is provided asensor device for monitoring the electrical status of an electricaldevice, the sensor device being attachable to a power cable of theelectrical device, and comprising an antenna element operable tomagnetically couple with an electrical pulse generated in the powercable to generate an electrical signal in response to a change in theelectrical power state of the electrical device; and a memory elementfor storing, in response to the generated electrical signal, datarepresentative of the power state change of the electrical device;wherein the antenna element is further operable to transmit datarepresentative of the electrical power state change of the electricaldevice and identification data identifying the sensor device to a readerdevice via the power supply cable.

According to a further aspect of the invention there is provided areader module for monitoring the electrical status of at least oneelectrical device connected to a power supply network by a respectivepower cable provided with a sensor device, the reader module beingoperable to transmit interrogation signals to one or more sensor devicesand to read identification data and electrical status data of one ormore sensor devices in response to the interrogation signals, eachsensor device being attached to a respective power cable of anelectrical device wherein the identification data and the status data isreceived from the respective sensor device through the power supplynetwork via the respective power cable, the electrical status data beingrepresentative of the change in electrical power state of the respectiveelectrical device; and the module being connected to a network interfacefor electrically coupling the reader module to the power supply networkand comprising means for extracting data signals received via the powersupply network and inserting interrogation signals for transmission viathe power supply network.

Some processes implemented by elements of the invention may be computerimplemented. Accordingly, such elements may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system’. Furthermore,such elements may take the form of a computer program product embodiedin any tangible medium of expression having computer usable program codeembodied in the medium.

Since elements of the present invention can be implemented in software,the present invention can be embodied as computer readable code forprovision to a programmable apparatus on any suitable carrier medium. Atangible carrier medium may comprise a storage medium such as a floppydisk, a CD-ROM, a hard disk drive, a magnetic tape device or a solidstate memory device and the like. A transient carrier medium may includea signal such as an electrical signal, an electronic signal, an opticalsignal, an acoustic signal, a magnetic signal or an electromagneticsignal, e.g. a microwave or RF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, and with reference to the following drawings in which:

FIG. 1 is a schematic block diagram of an electrical activity monitoringsystem in which one or more embodiments of the invention may beimplemented

FIG. 2 is a schematic block diagram of an RFID sensor device inaccordance with an embodiment of the invention;

FIG. 3A to 3C are schematic diagrams of an RFID sensor device inaccordance with different embodiments of the invention;

FIG. 4 is a schematic diagram illustrating an RFID sensor device inaccordance with an embodiment of the invention attached to the powercable of an electrical device;

FIG. 5A is a block functional diagram of elements of a RFID sensordevice in accordance with an embodiment of the invention;

FIG. 5B is a graphical diagram illustrating a signal processing processimplemented by an RFID sensor in accordance with an embodiment of theinvention;

FIG. 6 is a schematic block diagram of an electrical activity monitoringapparatus in accordance with an embodiment of the invention; and

FIG. 7 is a schematic block diagram of an RFID sensor device inaccordance with a further embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic block diagram of an electrical activity monitoringsystem in which one or more embodiments of the invention may beimplemented. The electrical activity monitoring system 100 monitors thechange in electrical status of n electrical devices 101_1 to 101 _(—) n.Each electrical device 101_1 to 101 _(—) n is connected by means of arespective electrical power cable 102_1 to 102 _(—) n to a power outlet103_1 to 103 _(—) n of an electrical power supply network 110. It willbe appreciated that while in the illustrated embodiment of FIG. 1 eachelectrical device 101_1 to 101 _(—) n is connected to a respective poweroutlet 103_1 to 103 _(—) n, in other embodiments of the invention aplurality of electrical devices may be connected to the same poweroutlet 103 _(—) x. Each electrical power cable 102_1 to 102 _(—) n isprovided with a respective RFID sensor unit 200_1 to 200 _(—) n. Theelectrical activity monitoring system 100 further includes an electricalactivity monitoring apparatus 300 connected to the power supply network110. The power supply network 110 is provided with a smart electricitymeter 400 for measuring electrical consumption in the power supplynetwork 110. The electrical activity monitoring apparatus 300 may beconnected to a communication network NET such as an Internet network sothat data on the electrical activity of the system may be transmitted toa remote server device, such as for example the server of an electricitypower supplier company.

FIG. 2 is a schematic block diagram of an RFID sensor device 200 inaccordance with an embodiment of the invention.

The RFID sensor device 200 comprises an antenna 210, a pulse detectionmodule 220 and a memory chip 230 for storing data representative of anelectrical status change. An RFID sensor device may also be referred toas an RFID tag, an RFID label, an RFID transponder and the like. Whilethe sensor device of FIG. 2 is an RFID sensor device it will beappreciated that in other embodiments of the invention the sensor devicemay be a sensor device comprising an antenna performing the functions ofthe embodiment of FIG. 2.

The antenna 210 has a dual function. Firstly, the antenna 210 of an RFIDsensor unit 200 _(—) x is used to detect the electrical pulse generatedin the respective power cable 102 _(—) x when the correspondingelectrical device 101 _(—) x undergoes a change in electrical powerstate, for example is switched ON or switched OFF. Indeed, the generatedelectrical pulse results from the change in power state of therespective electrical device 101 _(—) x. When an electrical device 101_(—) x is switched ON or OFF, a current pulse flows in its respectivepower cable 102 _(—) x. The antenna 210 of the respective RFID sensordevice 200 _(—) x attached to the power cable 102 _(—) x couplesmagnetically to the current pulse generating an electrical pulse whichcan be detected by the pulse detection module 220.

The second function of the antenna 210 is to transmit data from thememory chip 230 via the respective power cable 102 _(—) x to an RFIDreader of the monitoring device 300. Indeed the operating frequencyrange of the antenna 210 enables the performance of both functions ofimpulse detection by magnetic coupling and transmission of data to theRFID reader via the power cable. For example the RFID sensor device 200in this embodiment is a near field/short range RFID tag operating in theUHF frequency band, for example in the range from 800 MHz to 960 MHz,for instance in the region of 860 MHz or 900 MHz, or in the region of433 MHz or in the HF frequency band, for example in the region of 13.6MHz.

RFID is considered as a non specific short range device. It can usefrequency bands without a license. Nevertheless, RFID should typicallybe compliant with local regulations (ETSI, FCC etc.)

-   -   LF: 125 kHz-134.2 kHz: low frequencies,    -   HF: 13.56 MHz high frequencies,    -   UHF 860 MHz-960 MHz: ultra high frequencies,    -   SHF: 2.45 GHz: super high frequencies

Transmission of the data from the RFID sensor device 200 may be carriedout by backscattering through the power cable in response to aninterrogation from the RFID reader.

The memory chip 230 stores data indicating the change in electricalstatus of the corresponding electrical device 101 _(—) x. In someembodiments of the invention, the electrical voltage induced in theantenna 210 by the electrical pulse in the power cable 102 _(—) x anddetected by pulse detector 220 may be used to activate the memory chip230 to enable data to be stored. In the case of a passive type RFID tagthe antenna 210 acts as a power-coupling inductor which can harvestelectrical power from the current pulse in the power cable to operatethe modules of the RFID sensor device 200. Since the RFID sensor device200 in this particular embodiment is a passive RFID sensor device,energy consumption can be minimized since power is not being suppliedconstantly to the RFID sensor device 200 from a power supply such as abattery. It will be appreciated, however, that in alternativeembodiments of the invention the RFID sensor device 200 may be an activetype RFID tag powered by its own power supply means or a batteryassisted passive type RFID tag.

Each RFID sensor device 200 in the electrical monitoring system 100 isprovided with an identification code enabling the monitoring device 300to identify it.

The RFID sensor device 200 may be attached to the respective power cable102 _(—) x by any form of fixation means such as for example by adhesivesuch as glue, sticking tape, or a sticker, by a mechanical connectionsuch as for example staples, screws, nails; or by being embedded in theinsulating sheath cover of the respective power cable 102 _(—) x. In oneparticular embodiment, as illustrated in FIG. 3A, the RFID sensor device200A is provided in the form of a sticker with adhesive material 252Aprovided on the underside of the sticker to attach the sticker to therespective power cable 102 _(—) x while the antenna 210A, the pulsedetection module 220A and memory chip 230A are provided on the topsideof the sticker and covered by a protective cover layer 255A.

In some embodiments of the invention the antenna 210 may be shaped tofit around at least part of the power cable 102 _(—) x. In someembodiments of the invention, the antenna 210 of the RFID sensor device200 is in the form of a loop antenna and in use is arranged around atleast part of the respective power cable 102 _(—) x

FIG. 3B schematically illustrates examples of RFID near field UHF tags200B1 and 200B2 suitable for performing the dual functions of currentpulse detection and data transmission via the power cable. Each RFID tag200B1 and 200B2 respectively comprises a loop antenna element 210B1 and210B2, and an RFID memory chip 230B1 and 230B2. The RFID tags 200B1 and200B2 are attached to the respective cable 102-x with the respectiveantenna element 210B1 and 210B2 being arranged around at least part ofthe respective cable 102 _(—) x. In such a configuration the antenna210B1 or 210B2 may be attached to the exterior of the cable or embeddedin the cable.

FIG. 3C schematically illustrates examples of a RFID tag 200C1 and 200C2respectively provided with loop antennas 210C1, 210C2 and memory chips230C1 and 230C2 which may be employed in a particular embodiment of theinvention. The shapes of the loop antennas 210C1; 210C2 are configuredthe form factor of the power cable. This helps to ensure magneticcoupling with the current flow at HF or UHF frequencies.

FIG. 4 schematically illustrates the arrangement of an RFID sensordevice 200 attached to the power cable 102 of an electrical appliance101, in this example a hair dryer. The RFID sensor 200 is in the form ofa flexible sticker wrapped circumferentially around part of the powercable 102.

FIG. 5A is a schematic diagram illustrating an example of operation ofthe pulse detection module 220 of the RFID sensor device 200 in whichthe antenna 210 has the form of a loop antenna. A power state changepulse signal A is picked up by the loop antenna 210, by means of amagnetic coupling effect. When the amplitude of the power state changepulse signal A exceeds a predetermined threshold (1V for example), ablock comparator 221 detects an input pulse signal and in responsechanges the state of the output signal B. In order to avoid multitriggering, a temporization device 222 may be connected to the output ofthe comparator 221 to provide a signal C at its output which correspondsto the signal issued from the comparator during a set temporizationtime. A D flip flop module 223 generates a state bit D. The state bit Dis changed for each clocked impulse since the D Flip Flop module 223 isclocked by the output signal C of the temporization module 222.Consequently the last bit of bit signal D changes state at each detectedpulse (at switch on or off). The state can thus be used to indicate anelectrical power state change. The bit value is stored in the memorychip 230 of the RFID sensor device 200. This information representativeof a change of electrical power state of respective electrical device101 _(—) x can then be transmitted with the identification code ID RFIDsensor device 200 to the monitoring device 300. Signals A, B, C and D ofthe operation of FIG. 5A are graphically represented in FIG. 5B.

In particular embodiments of the invention by knowing the initialelectrical power state of the electrical device 101 _(—) x at counterreset, it is possible to determine from the state of bit signal Dwhether the electrical change corresponds to an ON/OFF electrical statuschange or an OFF/ON electrical status change. Moreover, by knowing theON or OFF power state of the electrical device at the previous readingthe ON or OFF power state at the subsequent reading can be deduced.

FIG. 6 is a block diagram schematically illustrating an electricalactivity monitoring apparatus 300 in accordance with an embodiment ofthe invention. The electrical activity monitoring apparatus 300comprises an RFID reader device 310 (also known as an RFID base stationor RFID transceiver), a power line interface device 320 and a monitoringdevice 330.

The RFID reader device 310 is a near field RFID type reader comprisingan RFID interface 311 for coupling to the power line interface device320 to receive RFID data signals from the RFID sensors 200 and to sendRFID interrogation signals (also known as excitation signals) to theRFID sensors 200 via power lines of the power line network 110; and anRFID processing device 312 for processing RFID data signals. The RFIDreader device 310 may be devoid of an RFID antenna, since communicationwith the RFID sensor devices 200 takes place via power lines of thepower supply network 110 rather than by wireless communication.

The power line interface device 320 comprises an RF transformer 321, apower transformer 322 and a DC voltage generator 323. RF transformer 321processes the HF or UHF RFID signal emitted by the RFID reader device321 so that the RFID signal couples with the power line to insert aninterrogation signal for transmission through the power lines to theRFID sensor devices 200.

The RF transformer is configured to perform transformation according tothe RFID operating frequency band HF, VHF or UHF. In order to maximizethe extension of coverage of the system transmission losses of the RFtransform are minimized. The RF transformer operates as an extractiondevice to extract the data signals from the power lines for reading bythe RFID reader 310, and as a signal insertion device to insertinterrogation signals from the RFID reader device into the powernetwork.

The power transformer 322 converts the AC voltage of the main power line110 to a secondary lower AC voltage. The DC voltage generator 323transforms the secondary lower AC voltage to DC voltages for the RFIDreader device 310 and the monitoring device 330.

Monitoring device 330 receives data from the RFID reader device 310indicative of the power state change activity status of the electricaldevices1 101_1 to 101 _(—) n in the electrical activity monitoringsystem 100.

In one particular embodiment of the invention the monitoring device 330is connected to a smart type electricity meter 400 connected to thepower supply network 110 of the system. The electricity meter 400 andthe monitoring 330 device may be connected by a wireless or wiredconnection. The smart electricity meter 400 is configured to monitor thepower consumption of electrical devices 101_1 to 101 _(—) n connected tothe power network 110. The smart electricity meter 400 is configured todetect a change in power consumption: for example an increase in therate of power consumption which may result from the switching ON of oneor more electrical devices 101_1 to 101 _(—) n supplied by the powernetwork 110, or a decrease in the rate of power consumption which mayresult from the switching OFF of one or more of the electrical devices101_1 to 101 _(—) n supplied by the power network 110. In response tothe detected change in power consumption a command signal is transmittedfrom the monitoring device 330 to the RFID reader device 310 to activatean RFID reading process. The RFID reader device 310 in response to thecommand signal transmits an interrogation signal to the RFID sensordevices 200_1 to 200 _(—) n in order to read the electrical status datastored in the respective RFID memory chips 230_1 to 230 _(—) n of theRFID sensor devices 200_1 to 200 _(—) n. The interrogation signal to besent from the RFID reader 310 to one or more RFID sensor devices 200 isinserted into the power network line signals by RF transformer 321 andpropagates along the power lines of the power network 110 to the powercables 102_1 to 102 _(—) n provided with RFID sensor devices 200_1 to200 _(—) n. The interrogation signals are then backscattered by the RFIDsensor devices 200_1 to 200 _(—) n along the power cables 102_1 to 102_(—) n towards the monitoring apparatus 300. The back scattered signalsfrom the RFID sensor devices 200_1 to 200 _(—) n each include theidentification code of the respective electrical devices 102_1 to 102_(—) n and the corresponding electrical power state change informationstored in the respective RFID memory chip 230. The collected electricalpower state change information signals are received at the interfacedevice 320 and transformed to be read by RFID processing module 312 ofRFID reader device 310. The processed electrical power state changeactivity information is then transmitted to the monitoring device 330.

Monitoring device 330 may further process the received power statechange information or transfer the power state change information toanother device, such as a remote device connected via a communicationnetwork.

For example, if an electrical device 101 _(—) x, for example a coffeemachine, connected to a household power supply network 110 is switchedON (for example from an OFF power state or from a STANDBY mode):

1. The total power consumption will increase by an amount correspondingto the power consumed by the coffee machine. This change in powerconsumption will be measured by smart electricity meter 400.

2. The current impulse generated in the corresponding power cable inresponse to the switch on activates the corresponding RFID sensor device200 attached to the respective power cable, and the status informationchange (OFF to ON) is stored in the RFID memory chip by switching a bit(the “state bit”) from 0 (corresponding to OFF state) to 1(corresponding to ON state)

The increase in power consumption measured by the smart electricitymeter 400 may be detected by the monitoring device 330. In response tothe detected increase a read command is sent to the RFID reader device300 to trigger a read phase of the RFID reader device 310. The RFIDreader module 310 reads all the RFID sensor devices 200_1 to 200 _(—) nof the electrical devices 101_1 to 101 _(—) n connected to the powernetwork 110 by transmitting interrogation signals. The read informationof each RFID sensor 200_1 and includes its identification and itselectrical ON/OFF change status.

In some embodiments of the invention by comparing the electrical changestatus of all the RFID sensor devices read with the previous one storedin an electrical devices status dataset, at the previous reading phase,it is possible to infer which electrical device has been powered on andthe electrical devices status dataset may be updated accordingly.

In other embodiments of the invention, the state of the respective statebit signal stored on the corresponding RFID memory chip can be used toidentify which electrical device or devices have been switched on oroff.

In some particular embodiments of the invention for an electrical devicean electrical pulse generated by an ON to OFF or STANDBY electricalpower state change, may be distinguished from an electrical pulsegenerated by an OFF or STANDBY to ON electrical power state change bycharacterizing the pulse signals. The impulse detector 220 of the RFIDsensor device 200 of such embodiments is configured to detect from thecharacteristics of the generated electrical pulse signal whether theelectrical pulse results from an ON to OFF or STANDBY power state changeor from an OFF or STANDBY to ON power state change.

In further embodiments the impulse detector may be configured todistinguish between an OFF to ON and a STANDBY to ON; and to distinguishbetween an ON to STANDBY and an ON to OFF, by characterizing theresulting pulse signals.

In another embodiment of the invention the power consumed by anelectrical device 101 _(—) x may be determined, for example by detectingan OFF to ON power state change or a standby to ON power state changeand then determining the duration of time for which the electricaldevice is placed in an ON state. Data representative of the powerconsumption may then be transferred from the corresponding RFID sensordevice 200 _(—) x to the RFID reader device 300 by means of the powernetwork 110 in the same way as data representative of the electricalpower state change is transmitted to the RFID reader device 300.

The electrical power state change data or consumption data may beprocessed to provide relevant information on electrical activity of thepower network 110, such as for example to build a household userprofile, to detect and warn of increased electrical power consumption,and/or to provide recommendations for reducing energy consumption

In other embodiments of the invention, rather than sending aninterrogation signal from the RFID reader to the RFID sensor devices inresponse to a command from the monitoring device 330 the RFID reader maysend interrogation signals automatically to the RFID sensor deviceswithout being commanded by the monitoring device; for example on aperiodic basis.

In some embodiments of the system that monitoring device may be part ofa home gateway system connected to an external internet network. Realtime tracking of the total home power consumption could be provided bythe home electricity provider via the internet network. For example theelectricity provider could trigger reading phases of the RFID reader bytransmitting signals from a remote server via the gateway device.

FIG. 7 is a schematic functional block diagram of an RFID sensor device700 in accordance with a further embodiment of the invention.

The RFID sensor device 700 comprises an antenna 710, a pulse detectionmodule 720 and a memory chip 730 for storing identification data of theRFID sensor and data representative of an electrical status change.These elements operate in a similar way to corresponding elements of theembodiment of FIG. 2. With respect to the embodiment of FIG. 2 the RFIDsensor device 700 further includes a timer 740. The timer 740 is used tomeasure the duration of time for which the electrical device has beenchanged electrical state by measuring the amount of time from when apulse was detected by the pulse detector 720. The time data may bestored in memory 730 and transmitted with the ID data and electricalstatus data to the RFID reader. The timing data enables the amount oftime a device has been switched on or off to be determined.

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

For instance, while the foregoing examples have been described withrespect to a household power network system, it will be appreciated thatembodiments of the invention may be applied to any power network towhich electrical devices are connected. Moreover the system could beapplied in security or safety applications to identify electricaldevices which have been changed electrical power state, such as beingswitched on or switched off.

Moreover while the embodiments have been described using an RFID tag andreader it will be appreciated that the invention may be applied to anysensor device comprising an antenna element and a corresponding readerdevice configured to communication with the sensor device.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

1. An electrical activity sensor device for monitoring the electricalstatus of an electrical device, the electrical activity sensor devicecomprising: a sensor device attachable to a power cable of theelectrical device, the sensor device including an antenna elementoperable to magnetically couple with an electrical pulse generated inthe power cable by a change in electrical power state of the electricaldevice to induce a detectable electrical signal; wherein the antennaelement is further operable to transmit data representative of the powerstate change of the electrical device to a reader device via the powercable.
 2. A device according to claim 1, wherein the antenna element hasa form factor adapted to the shape of the power cable.
 3. A deviceaccording to claim 1, wherein transmission of the data by the antennaelement comprises backscattering of an RF signal received from thereader device via the power cable
 4. A device according to claim 1,wherein the antenna element performs both magnetic coupling to theelectrical pulse and data transmission via the power supply cable withinits operating frequency range.
 5. A device according to claim 1 whereinthe sensor device comprises a memory element for storing, in response tothe detected electrical signal the data representative of the powerstate change of the electrical device and wherein the antenna element isconfigured to transmit identification data identifying the sensor deviceto the reader device.
 6. A device according to claim 1, wherein theantenna element is formed as a loop antenna.
 7. A device according toclaim 1, wherein the antenna element is configured to be arranged aroundat least part of the power supply cable to form an induction coil.
 8. Adevice according to claim 1 comprising a pulse detector configured todistinguish an electrical signal induced from switching on theelectrical device from an electrical signal induced from switching offthe electrical device.
 9. A device according to claim 1, wherein thesensor device comprises an RFID tag operable to communication with anRFID reader device.
 10. A device according to claim 9 wherein the RFIDsensor device is operable as a short range RFID tag.
 11. A deviceaccording to claim 1 wherein the sensor device is operable as a passivesensor device powered by electromagnetic induction via the power cable.12. A device according to claim 1 further comprising an electricalconsumption measurement module for providing data representative of thepower consumption of the electrical device when the electrical device isswitched on and wherein the data transmitted by the antenna elementincludes the data representative of the power consumption of theelectrical device.
 13. A device according to claim 1 further comprisinga timer to measure the duration of time since the detected change in theelectrical power state of the electrical device.
 14. An electricalactivity monitoring apparatus for monitoring the electrical status of atleast one electrical device connected to a power supply network by arespective power cable provided with a sensor device, the electricalactivity monitoring apparatus comprising: a reader module fortransmitting interrogation signals to one or more sensor devices and forreading electrical status data of one or more sensor devices in responseto the interrogation signals, each sensor device being attached to arespective power cable of an electrical device, wherein the electricalstatus data is received from the respective sensor device via therespective power cable, the electrical status data being representativeof an electrical power state change of the respective electrical device;and a network interface for electrically coupling the reader module tothe power supply network and comprising a signal for extracting datasignals received via the power supply network and insertinginterrogation signals for transmission via the power supply network. 15.An apparatus according to claim 14, wherein the reader module isconfigured to trigger the transmission of one or more interrogationsignals in response to a detected change in power consumption measuredby an electricity meter connected to the power supply network.
 16. Anapparatus according to claim 14 comprising a communication networkinterface for connecting with a communication network to enabletransmission of data to or reception of data from a remote serverconnected to the communication network.
 17. An apparatus according toclaim 14 wherein the reader module is configured to trigger thetransmission of one or more interrogation signals in response to acommand signal received via the communication network.
 18. An apparatusaccording to claim 14, wherein the reader module comprises an RFIDreader operable to communication with an RFID tag, the RFID reader beingoperable to receive RFID data from the RFID tag identifying the sensordevice.
 19. An electrical monitoring system comprising an electricalactivity monitoring apparatus according to claim
 14. 20. A gatewaysystem comprising an apparatus according to claim 14 and providing aninterface between an external data communication network and an internaldata communication network.